RTE Table Hash
These tables use the exact match criterion to uniquely associate data to lookup keys.
Hash table types:
- Entry add strategy on bucket full: a. Least Recently Used (LRU): One of the existing keys in the bucket is deleted and the new key is added in its place. The number of keys in each bucket never grows bigger than 4. The logic to pick the key to be dropped from the bucket is LRU. The hash table lookup operation maintains the order in which the keys in the same bucket are hit, so every time a key is hit, it becomes the new Most Recently Used (MRU) key, i.e. the most unlikely candidate for drop. When a key is added to the bucket, it also becomes the new MRU key. When a key needs to be picked and dropped, the most likely candidate for drop, i.e. the current LRU key, is always picked. The LRU logic requires maintaining specific data structures per each bucket. Use-cases: flow cache, etc. b. Extendible bucket (ext): The bucket is extended with space for 4 more keys. This is done by allocating additional memory at table init time, which is used to create a pool of free keys (the size of this pool is configurable and always a multiple of 4). On key add operation, the allocation of a group of 4 keys only happens successfully within the limit of free keys, otherwise the key add operation fails. On key delete operation, a group of 4 keys is freed back to the pool of free keys when the key to be deleted is the only key that was used within its group of 4 keys at that time. On key lookup operation, if the current bucket is in extended state and a match is not found in the first group of 4 keys, the search continues beyond the first group of 4 keys, potentially until all keys in this bucket are examined. The extendible bucket logic requires maintaining specific data structures per table and per each bucket. Use-cases: flow table, etc.
- Key size: a. Configurable key size b. Single key size (8-byte, 16-byte or 32-byte key size)
Definition in file rte_table_hash.h.